As the light emitting capabilities of Light Emitting Diodes (LEDs) continues to improve, their use in conventional lighting applications continues to increase, as do the competitive pressures to provide reliable, long-lasting products in a cost-effective manner. Even though the cost of LED products is relatively low, the savings of even a few cents per device can have a significant impact on profit margin, due to the increasingly growing market for these devices.
To reduce the cost of LED devices, copper can replace gold as the bulk metal for electrical contacts for LED dies. However gold still remains the preferred metal to provide efficient and reliable electrical and mechanical interconnections between the LED and its submount in a flip-chip configuration, wherein the upper layer of a LED die is attached to a submount, and light from the LED is emitted from a surface opposite the submount.
FIG. 1A illustrates a conventional flip-chip submount configuration of a light emitting device 100. The submount may include a base 110 upon which contacts 120 are formed; the contacts may be plated 125 to facilitate connections 145 to the flip chip contacts 150. The flip chip may comprise a growth substrate 170, a light emitting element 160, interconnect layers 165, and contacts 150. The growth substrate 170, commonly sapphire or other rigid material, may be removed after the flip chip is attached to the submount.
Two contacts 120 are illustrated in FIG. 1A, separated by a channel 130 that provides electrical isolation between the two contacts 120. In like manner, the contacts 150 are illustrated as being separated by a channel 135. The channel 135 may be smaller than the channel 130, in order to increase an amount of support provided to the interconnect layers 165 and light emitting element 170 by the contacts 150. This increased support may be particularly beneficial during the removal of the growth substrate 170. Also, the channel 130 may be larger than the channel 135 is order to accommodate potential alignment inaccuracy when the flip-chip is placed on the submount.
FIG. 1B illustrates an example thermal deformation 190 that may be caused when the light emitting device 100 is subject to high temperatures after the growth substrate 170 is removed. This deformation 190 may occur during manufacturing, and each time the light emitting device 100 is cycled from off to on. The deformation 190 may induce repeated stress to the interconnect layers 165 and the light emitting element 160, and may cause the device 100 to fail prematurely. Additionally, the upper layer 175 of the light emitting device may be etched to increase the light extraction efficiency of the light emitting element 170, which may cause the upper layer 175 to be more susceptible to stress induced failures.